Answers and explanations · Compare groups without turning a p-value into a verdict

Lesson 8 answers

8A. “The checklist group averaged 3.2015 minutes less than control, a checklist−control difference of −3.2015. The 95% Welch interval was [−5.8496,−0.5534] minutes and the two-sided p-value was 0.0191 under the equal-mean null model. The calculation assumes independent outcomes from the specified model, and the entirely simulated study provides no direct evidence of real operational effectiveness.” Rounded equivalents are appropriate in a management brief.

8B. No. The interval permits a 6-minute reduction and a 4-minute increase. Non-rejection of zero does not establish equality, absence of a useful effect or equivalence. An equivalence claim needs a justified pre-specified acceptable range and a method designed for that claim.

8C. Different independent people in two assigned groups can fit Welch's setup if outcome assumptions are suitable. Before/after data from the same people are paired and need a method respecting those pairs. Team-randomized tasks are clustered at the assignment unit; an independent-task Welch analysis ignores team dependence. Changing the numerical method does not fix a flawed recruitment or measurement process.